THE DIAPHRAGM. 197 



Chapter XL 

 THE BELLY AND ITS CONTENTS. 



THE DIAPHRAGM. 



The chest is separated from the abdomen or belly, by the diaphragm or 

 midriff, which extends obliquely from the loins to the breast-bone. In its 

 natural state it is convex, or projecting forward towards the lungs, and 

 concave or hollow backward towards the stomach and intestines. On the 

 side towards the chest it is covered by the membrane which invests the 

 lungs, and towards the belly by that which covers the intestines. It 

 is attached to the spine, the ribs, and the breast-bone by tendinous or 

 fleshy expansions, and in the centre it is composed of strong muscular 

 fibres. It is one of the most important muscles of the frame. It is, as we 

 have described it, the principal agent in breathing. When it acts, its 

 fibres are shortened ; it loses its convexity and becomes plane ; the chest is 

 thereby enlarged, and the lungs enlarge with the expansion of the cavity in 

 which they are placed ; and air rushes in, and inspiration is performed. 

 When the fibres of the diaphragm cease to act, that muscle returns to its 

 natural form ; it becomes again convex ; it presses upon the lungs, and 

 helps to force out the air, and expiration is accomplished. It assists like- 

 wise in the natural constant motion of the bowels, and lends its powerful 

 aid in the expulsion of the dung and urine, and in the birth of the young 

 animal. It is most concerned in coughing, yawning, sighing, &c. The 

 membrane which covers the diaphragm is very subject to inflammation. 

 Whether the original seat of disease be in the lungs or the bowels, the 

 diaphragm soon becomes inflamed and irritable, which accounts for the 

 breathing of the horse being so much affected under every inflammation of 

 the chest or belly. The diaphragm is likewise occasionally ruptured, 

 principally from violent exertion. It has so much to do in the act of 

 breathing, that it is not to be wondered if, when the respiration is exceed- 

 ingly hurried, this muscle should give way. The symptoms of ruptured 

 diaphragm are very obscure. There are none on which we can perfectly 

 depend. This, however, is a matter of litde consequence, for it is uni- 

 formly fatal. If the rupture be small, some portion of the intestines 

 insinuates itself, and becomes entangled, and the passage is incurably 

 obstructed ; and if the aperture be large, so much of the intestine passes 

 through as to press upon the lungs, and render breathing impossible. 



Three large vessels pass through the diaphragm ; the great artery which 

 conveys the blood from the heart to the hinder part of the frame, and which 

 goes through a kind of division of the diaphragm, so that it cannot be 

 pressed upon ; the great vein carrying the blood from the hinder parts and 

 the liver to the heart, and which penetrates the firm tendinous part of the 

 diaphragm so as likewise to be preserved from pressure ; and the gullet, 

 which passes through the most fleshy portion of the diaphragm, and is liable 

 to be compressed by the constant action of this muscle, which, however, is 

 a matter of httle consequence, for there is sufficient power in the muscles 

 of the gullet to propel the food through the diaphragm into the stomach. 



The gullet terminates in 



